1. Field of the Invention
The present invention relates to a developing roller used for an electrophotographic apparatus, a process cartridge having the developing roller, and an electrophotographic apparatus.
2. Description of the Related Art
In electrophotographic apparatuses (such as copiers, fax machines, and printers using electrophotography), an electrophotographic photosensitive member (hereinafter, also referred to as a “photosensitive member”) is charged by a charging unit, and exposed by a laser or the like to form an electrostatic latent image on the photosensitive member. Next, a toner in a developing container is applied onto a developing roller by a toner feeding roller and a toner controlling member. By the toner conveyed by the developing roller to a region to be developed, an electrostatic latent image on the photosensitive member is developed in a contact portion between the photosensitive member and the developing roller or a portion in the vicinity thereof. Subsequently, the toner on the photosensitive member is transferred onto a recording paper by a transferring unit, and fixed by heat and pressure. The remaining toner on the photosensitive member is removed by a cleaning blade.
As the developing roller, an elastic roller having an electric resistance of 103 to 1010 Ω·cm is usually used. Moreover, in consideration of a demand for higher durability of the developing roller and higher quality of the electrophotographic image, a developing roller provided with a surface layer on the surface of the elastic layer is used.
Here, as the elastic layer of the developing roller, silicone rubbers having high deformation recoverability and flexibility are suitably used. As the surface layer, polyurethanes having high resistance to wear and toner charging properties are used.
Japanese Patent Application Laid-Open No. 2005-141192 discloses a method in which a poly (tetramethylene glycol) polyurethane surface layer comprising a specific composition is provided on a silicone rubber elastic layer to suppress problems under various environments of temperature and humidity. Japanese Patent Application Laid-Open No. 2006-251342 discloses a composition of a polyether polyurethane surface layer that can suppress fusing of a low melting point toner.
Further, Japanese Patent Application Laid-Open No. H07-199645 discloses a developing roller using a polyurethane surface layer having a low water absorption rate in order to keep charging properties under a high temperature and high humidity environment.